Welcome to HVAC-Talk.com, a non-DIY site and the ultimate Source for HVAC Information & Knowledge Sharing for the industry professional! Here you can join over 150,000 HVAC Professionals & enthusiasts from around the world discussing all things related to HVAC/R. You are currently viewing as a NON-REGISTERED guest which gives you limited access to view discussions

To gain full access to our forums you must register; for a free account. As a registered Guest you will be able to:

Participate in over 40 different forums and search/browse from nearly 3 million posts.

This past Friday (7/15/05), the installation of my Carrier Infinity 96 Gas Furnace and Infinity 18 Air Conditioner was completed. This was my first HVAC purchase of my lifetime. I am having buyer’s remorse and believe I should have put more time into researching my options BEFORE and not after my purchase (Like I have been since the installation). I live in Western PA and my 20-year-old Bryant furnace (90K BTU?) had needed too many repairs the last few years, so I decided to replace it. My Bryant A/C (2.5 ton) seemed to work fine, but I felt it would be best to replace it since it was also 20 years old.

I only obtained two quotes: a lennox dealer quoted the 90K BTU G43 and Merit Series 10 ACC (3 ton). The Carrier dealer quoted me the Infinity System. I was too DUMB to ask the Carrier dealer about BTUs and tons. After spending several hours on this site and others, I think I understand (a little bit) about some of this HVAC terminology.

I decided to go with the Carrier quote due to a recommendation from a friend/builder and the dealer’s reputation for quality work, despite a $2000 difference. Also, the sales rep sold me on the high efficiency, two-stage, variable speed hoopla! (My old Bryant cycled off and on every 60 seconds in winter). After checking my model numbers on the Carrier website, I see that I was sold the 58MVP060-14 (60K BTU) and the 38TDB024 (2 ton).

I am unhappy with the cooling performance of the system. On Friday at 4:00 pm the installation was completed. At that time, the indoor temp was 87 (outdoor - 90). The temp only dropped one degree per hour and by 9:00 pm; it was still 83 on my first floor, 88 on the second floor (Cape Cod style house – my second floor never gets below 80). By 3:00 am, it finally dropped to 74. I have set the target temp to 72, just as an experiment. THE UNIT CANNOT GET THE TEMP BELOW 74, EVEN ON HIGH FAN SPEED. Today (Sunday) with the fan speed set to high, the temp was 77 at noon, stayed at 76 until 7:00 pm, and then dropped to 75 at 8:00 pm (outdoor was 93 at noon, 75 at 8:00 pm). Last night I took the following readings: LR supply temp – 55, BR supply – 60, 2nd Flr Bath supply – 64, LR return – 70.

While I am not an Eskimo and would rarely have my target temp at 72, my concern is the time it takes to reach the target temp and my inability to get my second floor below 80. The airflow coming out of the registers seems too weak. While my old Bryant sounded like a jet engine, that sucker blasted cold air and cooled the downstairs very fast! Even the installers said the register airflow seemed weak, but said the system was running perfect, based on the readouts from their equipment and the thermostat. They did however; remind me that my basement ductwork was abnormally large (main supply is 31” x 8” extending approximately 13 feet before branching off into smaller runs). I assume they will try and tell me my ductwork is the problem.

My bottom line question is: Is this system undersized for my home (1800 SF Cape Cod w/ unfinished basement) and ductwork issues? It seems to me that the blower isn’t pushing enough air to cool properly. Do I need a larger A/C, furnace or both? The lennox dealer quoted larger units and the ones pulled out of my house were larger units. I don’t know how the Carrier salesman calculated my system needs; I didn’t even know what manual J was until I investigated this site. He took rough measurements of the outside of the house and sent me the estimate in the mail.

I spoke to the Carrier salesman today and expressed my concern. They are sending a technician out to check my system early this week. Since I am just an uneducated HVAC consumer, what advice can anyone give me before I meet with the technician?

Sorry for the extra long post, but I wanted to provide enough data to describe my situation.

No problem on the long post. Good information. Here's what I see here.

First lets discuss WHAT YOU SAID about your - OLD - system.

1. It sounded like a jet
2. It cooled the downstairs very fast.
3. Air "blasted" out of the registers
4. (winter) the heater cycled every 60 seconds (I take that to mean it cycled often).

Based on those things said above, I believe that your old sytem MAY have been over-sized. Don't scream yet, let me explain...

Lets take it point by point....

1. "It soundd like a jet". I am not sure what you mean by this but I assume that the system was noisy, especially at the return. (The return is where the system takes air in.) 9 times of 10, when a system is noisy at the return, it is because of a system that is too large for that return and has to try hard to pull enough air through it.

2. "It cooled the downstairs very fast" and "air rushed from the registers". An airconditioner is supposed to cool AND DEHUMIDIFY a house. When it cools a house extremely fast (say bringing the temp down within an hour and a half)the unit does not have a chance to remove much humidity from the house.

This is most often the case with an over sized airconditioner that blows so much cool air in, the thermostat is satisfied quickly and shuts the unit off.

3. "The old heater used to cycle every 60 seconds". Again, the heater shouldn't sycle this quickly either. Furnaces that heat a house quickly and have excessively strong air flow are likely over-sized.

The above reasons are why I think your old system may have been over-sized and why I believe you should not use it as a control to which to compare your new system.

That being said, you shouldn't have buyer's remorse and you got a great system. And, once you do the things below, you should be on your way to being happier.

1. To put the size issue at rest once and for all, PLEASE, PLEASE (PLEASE) click on the HVAC-CALC software link within this site and buy the software. I think it is 50 bucks but c'mon, you ALREADY are in this project $3,xxx.xx so spend 50 more. It is worth it.

With HVAC-CALC, you can run your own load calculation on your home and determine what size you need. Most contractors worth their salt should do load calculations on replacements and determine sizing that way. They should conclude that the size of existing equipment is irrelevent (sp). Most EXCEPTIONAL contractors do this and you should too. HVAC-CALC was developed by a member here and is easy to use for homeowners and professionals alike.

Run a load calculation and find out what size you need (and if the Carrier guy put in the right size).

2. Once you determine the size of the equipment needed, you may or may not have the right size furnace and A/C.

Assuming you have (or get) the right sized stuff, you MAY need duct work done. This is normal as 20 years ago, they did not know as much as ductwork as they do now. They also did not have the technology they do now (i.e, was your Infinity system around 20 years ago? Nope.) Sometimes OLD ductwork and new technology just don't mix well w/o some changes.

Listen to your contractor and see what he has to say about ductwork.

Things I would ask about if it were my home....

1. Locate a return UPSTAIRS in the ceiling. You complained that the upstairs never got below 88. Putting a SECOND return up there would help. I assume you don't have a return there and the one you have is down stairs. Most 20 year old "cods" didn't have returns upstairs. THIS RETURN IS AN ADDITION (NOT REPLACEMENT) FOR THE ONE DOWNSTAIRS.

2. Week airflow. Ducting issue. Ductwork that is too large might have stattic pressure issues and not work properly. The fact that this ductwork is too large lends to the theory that your old system was too big.

I hope this helps.

I encourage you to buy the software mentioned above and do this the right and informed way. Your home is an investment and remember this, any money spent on improvements like this comes back (oftem many times over) later as equity.

balystic took the time to give you a decent response.I would like to add give the service guys a chance to go over the system.they may find some installation issues that need addressed or some duct issues that need addressed.messing with the fan speed is not a good idea.If you move more air than needed for the system you will decrease dehumidification & comfort levels in your home.also remember that this new system is not it's grandfather or even it's father-If you do not have annualclean & checks expect problems in the future.

It's unlikely the ducts are too large,they can check the static ,on the system with the Infinity control and tell easily.

The Infinity ,will run in low,by design,in most cases ,most of the time.Remember that's 50% capacity,so it's economical,as well as better for comfort and the compressor.

The second floor likely needs more supply air.If it cools properly with the doors open,then it needs a return or return path.If it doesn't cool properly with the doors open,it needs more supply air,and could need a return or return path for operation with the doors closed.

A return to the upper floor is a good idea,but the location ,high or low,has little effect on comfort.The supply grilles ,throw(how far the air travels),location ,and type will determine comfort.

Did you not have a temerature difference between floors ,before,as it's very common,without two systems ,zoning,or manual dampers to seasonally adjust the air flow to each floor.

The air flow or lack of,to the upper floor is probably to to the size of the ducts and the overall static of the duct system,reducing the static,larger ducts,adding turning vanes ,etc.,will allow more air flow.

What temerature could you maintain before?In our area the standard is 78°F ,and in some cases people want 75°.Are you uncomfortable ,or just looking at the stat and the run times?

If it is undersized ,for the temerature desired ,have them do a load calculation,which should and may have been done,especially when installing a smaller or larger system, then the old one.Then look at adding insulation to the attic or tinting east/west glass,to reduce the needed capacity,instead of going to a larger system,more operating cost savings doing it that way.

Are you sure the thermostat was set up properly? There are tiny switches that must be set properly. I was having cooling problems on my Carrier system and it turned out one of the switches wasn't set for two-stage cooling and it was only running on low. The default is one-stage. You should hear the blower going from low to high. It starts out on low. It's very noticeable.

Don't panic. Give the contractor a chance to sort things out. My experience with system replacements indicates that the first day is a rush to get to where you have a viable system, and then they expect to come back in a day or two to do the fine tuning. You are still well within the fine tuning phase, so it's not time to worry (yet).

It sounds like you have a problem getting air to the upstairs, which may or may not be simple to correct. It's very rare that a two story home with a single system can have even temperatures on both floors without zone control, though, so don't expect the new system to improve much on that front.

Nothing about heating or especially air conditioning is supposed to be fast. It should just be able to keep up on a typical summer afternoon. If it's sized to do things quickly, it's not going to control humidity well and will never deliver the rated efficiency. In hot weather, that does mean that the system should run almost nonstop. A small unit running all the time is more much efficient than one with twice the rated capacity running half the time, and will produce a much more comfortable indoor enviroment, too. With a two-speed system like yours, in the heat of summer, it may end up that the system does in fact run around the clock for days or weeks, running on high except for a few hours on low in the middle of the night.

The fan speed control (low, medium, high, auto) you see on the unit only affects what the fan does when there is no heating or cooling going on already- many people misunderstand that. During cooling season, you should leave the fan speed setting on Auto unless you have a specific reason to do otherwise- and even then be prepared for humidity control to suffer, and to pay some penalty in energy consumption. The system tries to avoid it, but some moisture from the coil will still evaporate back into the house whenever there is airflow in the absence of cooling. Once it evaporates, it's just more work for the system to do to condense it again. If the coil is cold whenever there is airflow across it, the only place that condensation is going to go is down the drain, and that's where we want it.

Finally, the Infinity system controls temperature and humidity together, as an integral issue, to produce a comfort outcome. It's easier to see what it's doing with the temperature, though. What we mean in this sense is that 76 degrees feels nice at 48% humidity, but 74 feels hot at 65% humidity. If you started the system up on Friday after having gone without AC for awhile, it has a lot of work to do- not only with cooling, but in humidity removal. Particularly once it gets close to the temperature setpoint, if the house has gotten humid inside, it may take several days to get the humidity completely under control. During that time, it will balance the need for cooling and dehumidification as best it can to produce comfort, even if that means that it may take longer to get to the temperature setpoint. Once it gets there, though, it's much easier to hold its ground.

[Faulty weather data removed by wyounger. Oops.]

It can be hard to tell when a two-speed Infinity system is running high or low speed, if there ductwork isn't noisy. The LED on the control unit will pulse slowly during low cool and quickly during high cool, though.

DOWNSTAIRS:
LR (13x19) - two supply and two return (coolest room in the house, directly above the furnace)
DR (12x12) - one supply and one return, which is where the thermostat is mounted.
½ Bath – one supply
Kitchen – one supply
Sunroom - two supply and one return

I found my old house inspection from 1988 and it stated that my Bryant furnace was 71K BTUs, not 90K as earlier thought. Attic insulation is 6” of vermiculite and fiberglass batts, no insulation in the exterior walls (plaster and brick).

Yes, my old furnace cycled quite a bit, on a cold day, it would come back on within 30-60 seconds. My gas bills averaged $270 from Dec – March (stat btw 68-71), even with new windows installed three summers ago.

When I say Jet engine, the old A/C & furnace (blower) made a lot of noise coming out of the LR register closest to the furnace. I can barely hear this new Carrier system. While the old system cooled the downstairs fast, I still could not get the upstairs cool enough (even by closing the downstairs registers). Without a ceiling fan in the Master BR and a portable GE 10K BTU A/C in my spare BR (now an office with a computer), it would be unbearable in the upstairs. As it is, after a shower, all you do is sweat (if you stay in the bathroom). Sorry for the image, but I have to go in my spare BR NAKED and stand in front of the portable A/C to stop sweating.

Now, I was hoping all this would change after sinking a sizable chunk of money into my new Carrier system. I would hope that the system might have stabilized by now. The humidity readings have been high 30’s and low 40’s on the stat the last 24 hr. I even have a dehumidifier in the basement that I empty twice a day.

When I got home today, the temp was at last night’s set point (new term I learned from this forum) of 78. I lowered it to 76. Two hours later, it is still 78 (78 outside, 40% hum inside). The led light is blinking slowly, so I assume it is running on low (I switched the fan from high to auto last night). You can barely feel any air coming from the registers, except the one closest to the furnace.

Sorry to be so long-winded again, so to summarize my two concerns:

1st Concern: My wife and I give private dance lessons in our LR; we are happy to keep the stat at 77-78 most of the time, but when someone is coming for a lesson, we drop the stat about four degrees an hour or two before the lesson. My old unit had no problem hitting the set point very quickly. I understand the inefficiency and lack of humidity control with a fast system, but come on, I could have bought ½ of a new (cheap) car for what this system cost me and I have to wait hours and hours for it to drop 1 degree?

2nd Concern: I had hoped that for all the dough I spent, I could close my first floor registers and achieve some kind of comfort in my upstairs. At this rate, I think I have to close my upstairs registers in hopes of reaching the set point downstairs before summer is over.

Sorry for the sarcasm, but when you spend this kind of money, you expect a bit more performance.

I will be patient and see what happens after the technician comes tomorrow. Thanks for listening to my gripes.